1. Field of the Invention
This invention relates to a steam turbine power generation system, and in particular, to an apparatus associated therewith to indicate moisture presence within the steam flow.
2. Description of the Prior Art
The incidence of turbine damage due to the induction of water into the turbine element is an increasing phenomenon in power generation industry. When water enters the turbine serious damage often can occur, often requiring extended periods of turbine inactivity in order to make necessary repairs. The magnitude of the problem has been recognized and appreciated by those in the power generation industry, and has led to the formation of a Turbine Water Damage Prevention Committee Standards Department of the American Society of Mechanical Engineers.
The identification of the causal factors leading to the increase in turbine water damage is difficult. However, whatever the reasons responsible for the creation of water in the vapor flow, one important preventative measure recommended by the Prevention Committee, and embodied in the Standards issued thereby, is the use of apparatus which is able to detect the presence of water droplets in the vapor flow in order to avoid the damage to turbine occasioned thereby.
In the prior art, thermocouple devices are disposed within the turbine cylinder, in the inlet piping, and in other conduit lines leading to the apparatus. However, for the cylinder thermocouple, it is the unfortunate case that the indication of water droplets occurs at a time when damage to the turbine is unavoidable. Similarly, the use of thermocouples in the inlet and extraction lines or other piping leading into the turbine to detect the presence of water therein by the detection of the metal temperature is also of limited value. This is so since, once the metal temperature of the conduit has been lowered sufficiently to substantiate that water droplets or cool vapor is carried within the vapor flow, there is little action that can be taken in time to prevent turbine damage. Also, the disposition of thermocouples within the turbine piping is disadvantageous from a mechanical standpoint. The thermocouples are usually mounted in an intrusive manner, that is, into the body of the piping itself. This leads to local mechanical weakness and is, for this reason, undesirable.
It is apparent that a detection system to detect the presence of moisture droplets within a steam vapor flow within the conduit leading to the turbine so as to prevent water damage thereto is desirable. Such a system must be able to quickly ascertain the presence of the liquid droplets and relay this data to the turbine control system in sufficient time to effectively prevent water damage. The system must be reliable and accurate so that "false alarm" rate is low enough to insure that repeated false shutdowns of the turbine are avoided. Further, the apparatus must preferably obtain the necessary information without intrusive mounting into the conduit so as to avoid mechanical damage thereto. Also, indications as to the quality of the steam conducted within the conduit would be an advantageous and desirable capability for such apparatus.